This rendering depicts what RockBridge Capital LLC and its partners hope to develop at what is now the publicly owned Congress Square Plaza.

PORTLAND, Maine — After nearly three months of negotiation and public debate, the city has reached a tentative agreement to sell two-thirds of Congress Square Plaza to the owner of the former Eastland Park Hotel.

RockBridge Capital LLC would pay more than $523,600 for about 9,500 square feet of the public space at the corner of Congress and High streets, according to a memo released Friday by Greg Mitchell, the city’s director of economic development.

The purchase price is based on a market appraisal of $55.12 per square foot.

If the sale is completed, about 4,800 square feet of the plaza would remain as public space.

RockBridge and co-developer New Castle Hotels & Resorts are finishing a $50 million renovation of the historic hotel and plan to reopen it in December as the Westin Portland Harborview Hotel. The developers have hoped to acquire a portion of the plaza to build an adjoining center for meetings and events.

Under terms of the draft agreement, RockBridge must continue to use the center for that purpose for 10 years. Afterward, the space could be converted to “uses customarily found in hotels.”

The City Council’s Housing and Community Development Committee voted, 3-1, on May 29 to negotiate the sale of the property.

The committee will consider the draft agreement at a meeting Wednesday, Aug. 21. It may then make a recommendation to the City Council, which has the final decision-making authority on the sale of city property.

The committee meeting is scheduled for 5:30 p.m. in City Council chambers.